The invention relates to a monolith catalyst and to the use thereof for petrochemical conversions such as dehydrogenations, aromatizations, reformings and combustions.
In numerous petrochemical reactions (for example dehydrogenations, aromatizations, reformings and combustions), supported noble metal catalysts are used. The use of such catalysts is very expensive owing to high noble metal costs. In addition, unfavorable noble metal distribution and long diffusion pathways in conventional catalysts lead to low noble metal exploitation.
U.S. Pat. No. 4,788,371 describes a process for steam dehydrogenation of dehydrogenatable hydrocarbons in the gas phase combined with oxidative reheating of the intermediates, with the same catalyst being used for the selective oxidation of hydrogen and the steam dehydrogenation. Here, hydrogen can be introduced as co-feed. The catalyst used comprises a noble metal of group VIII, an alkali metal and a further metal selected from the group consisting of B, Ga, In, Ge, Sn and Pb on an inorganic oxide support such as aluminum oxide. The process can be carried out in one or more stages in a fixed or moving bed.
WO 94/29021 describes a catalyst which comprises a support consisting essentially of a mixed oxide of magnesium and aluminum Mg(Al)O and also a noble metal of group VIII, preferably platinum, a metal of group IVA, preferably tin, and possibly an alkali metal, preferably cesium. The catalyst is used in the dehydrogenation of hydrocarbons, which can be carried out in the presence of oxygen.
U.S. Pat. No. 5,733,518 describes a process for the selective oxidation of hydrogen by oxygen in the presence of hydrocarbons such as n-butane over a catalyst comprising a phosphate of germanium, tin, lead, arsenic, antimony or bismuth, preferably tin. The combustion of the hydrogen generates, in at least one reaction zone, the heat of reaction necessary for the endothermic dehydrogenation.
EP-A 0 838 534 describes a catalyst for the steam-free hydrogenation of alkanes, in particular isobutane, in the presence of oxygen. The catalyst used comprises a platinum group metal applied to a support comprising tin oxide/zirconium oxide and having a tin content of at least 10%. The oxygen content of the feed stream for the dehydrogenation is calculated so that the quantity of heat generated by the combustion reaction of hydrogen and oxygen is equal to the quantity of heat required for the dehydrogenation.
WO 96/33151 describes a process for the dehydrogenation of a C2-C5-alkane in the absence of oxygen over a dehydrogenation catalyst comprising Cr, Mo, Ga, Zn or a group VIII metal with simultaneous oxidation of the resulting hydrogen over a reducible metal oxide, e.g. an oxide of Bi, In, Sb, Zn, Tl, Pb or Te. The dehydrogenation has to be interrupted at regular intervals in order to reoxidize the reduced oxide by means of an oxygen source. U.S. Pat. No. 5,430,209 describes a corresponding process in which the dehydrogenation step and the oxidation step proceed sequentially and the associated catalysts are separated physically from one another. Catalysts used for the selective oxidation of hydrogen are oxides of Bi, Sb and Te and also their mixed oxides.
Finally, WO 96/33150 describes a process in which a C2-C5 alkane is dehydrogenated over a dehydrogenation catalyst in a first stage, the output gas from the dehydrogenation stage is mixed with oxygen and, in a second stage, passed over an oxidation catalyst, preferably Bi2O3, so as to selectively oxidize the hydrogen formed to water, and, in a third stage, the output gas from the second stage is again passed over a dehydrogenation catalyst.
It is known that aromatic hydrocarbons can be obtained by catalytic dehydrogenating aromatization of open-chain hydrocarbons (see, for example, Catalysis VI, p. 535-542, ed. by P. H. Emmet, Reinhold Publishing Co., New York, 1958).
U.S. Pat. No. 3,449,461 describes the dehydrogenating aromatization of open-chain C6 to C20 paraffins to aromatic hydrocarbons including o-xylene with the aid of a sulfur catalyst which comprises a noble metal such as palladium or platinum.
US-A 2004/0044261 describes a process for selectively preparing p-xylene by converting C8 isoalkenes or alkenes over a catalyst which comprises a molecular sieve laden with a noble metal of transition group VIII.
DE-A 197 27 021 describes a process for preparing C8 aromatics from butenes by dehydrogenating olefinically unsaturated C8 hydrocarbon mixtures obtainable by dimerizing technical C4 cuts over a catalyst which comprises at least one element of the platinum group on an amphoteric ceramic support. The main reaction product is ethylbenzene; in addition, o-xylene is also formed.